1. Field of Invention
The present invention relates to electrodes used in resistance welding. The electrode tip has grooves that lock onto a metal pin which has been inserted in the electrode. The locking mechanism prevents workpiece metal from sticking to the tip; causing the tip to dislodge from the electrode. The locking mechanism eliminates the need for continuous reattachment of the electrode tip to the electrode and thereby facilitates production line flow and extends the useful life of the electrode.
2. Description of Prior Art
Resistance welding electrodes are widely used in industry for spot welding steel, aluminum, copper, and various other metals. Some particular applications are the assembly of automobile bodies and truck bodies. In each of these uses, a robot weld gun fitted with a pair of electrodes is moved in stages along a continuous weld path. At each stage, the electrodes are contacted with opposite sides of the workpieces to be welded, and an electric current is passed through the electrodes and workpieces. Electrical resistance of the metals produces localized heating which causes the workpieces to fuse at a weld site. To prevent the electrodes from softening and melting, cooling water is continuously circulated through them at high pressure. When performed on a production line, these steps are each performed in rapid sequence and they are repeated at several different weld stations.
The electrodes are generally made from copper or copper alloys for low electrical resistivity and high current flow. The tips are also made from copper or copper alloys for high electrical conductivity. Frequently, the electrode tip sticks to the workpiece and dislodges the tip from the electrode. Also, repeated impact of the electrode tip to the workpiece loosens the contact tip from the electrode and can cause the electrode tip to dislodge. This common phenomenon causes the production line to shut down while the tips are manually reattached to the electrode.
There is no prior art that directly applies to the retention of the electrode contact tip on the electrode shank during resistance spot welding. Although some coatings have been developed in the prior art in order to prevent the workpiece metal and the electrode tip from sticking to each other. For example, Huys U.S. Pat. No. 4,861,961 discloses a welding electrode coated with titanium carbide. Engel U.S. Pat. No. 3,665,145 and Glagola U.S. Pat. No. 4,044,220 both disclose welding electrodes coated with nickel, beryllium, cobalt, iron, and alloys of such metals.
Lambert U.S. Pat. No. 2,431,334 claims a welding electrode comprising a tungsten rod coated with tungsten carbide. Anderson U.S. Pat. No. 5,066,845 discloses a welding electrode coated with tungsten disulfide. Although the above mentioned patents prevent workpiece metal from sticking to the electrode tip they do not prevent the tip from dislodging from the electrode itself.
Lajoie U.S. Pat. No. 5,726,420 discloses a taper lock contact tip for a welding device. The taper lock system has been designed specifically for metal inert gas welding equipment.
The above mentioned patent cannot be utilized for resistance spot welding due to three reasons. First, the threaded design compromises the structural integrity of the electrode and can cause fractures or breakage of the electrode due to the thinner walls and repeated impact during resistance spot welding. Second, because the inside of the electrode is continuously circulated with high pressure water as a cooling mechanism, the threaded taper lock can create an increased probability of water leakage. Third, the electrode tips are continuously changed throughout the day and repeated removal and attachment of electrode tips will cause premature wear of the threads which will shorten the useful life of the electrode.